A method for spinning and blending two or more kinds of filaments having a large heat shrinkage difference therebetween has been known as a method for obtaining a spun blended yarn, and said blended yarn can thermally be treated to give the bulky yarn. As a concrete method for developing the above-described heat shrinkage difference, a method using two kinds of polymers having a viscosity difference, a method using a polymer copolymerized with the third component as one of two kinds of the polymers, and the like have been proposed. However, all of these methods are based on crystal orientation differences due to the differences of molecular structures. Therefore, even when a large heat shrinkage difference has been developed, a sufficiently large elongation difference has still not been developed.
For example, in JP-A 54-82423 (hereunder, JP-A means “Japanese Unexamined Patent Publication”) has been proposed a method for melting and extruding a polyester from an identical spinneret, quenching the obtained filaments, dividing the filaments into two groups, imparting an oiling agent consisting mainly of water to one of the obtained filament bundles, imparting an oiling agent having a higher boiling point than that of the water to the other, separately thermally treating both the filament bundles in the same condition, simultaneously drawing the filament bundles, and then blending both the filament bundles. But, since a boiling point difference between the spinning oiling agents is utilized to impart a shrinkage difference (boiling water shrinkage difference) between the filament bundles in this method, the boiling water shrinkage difference between said filament bundles can sufficiently not be enlarged, and the obtained blended yarn has a small shrinkage difference between the filaments. Therefore, the finally obtained woven fabric is poorly swollen, and a satisfiable woven fabric can be obtained.
Additionally, in JP-A 58-191211 has been described a blended yarn characterized by melt-extruding two multifilament yarns from an identical spinning pack, giving a difference between a bundling position for one multifilament yarn and a bundling position for the other multifilament yarn, taking off the multifilament yarns at a take-off speed of not less than 4,500 m/min, developing an air resistance difference on said take-off operation to blend and winding up the yarns, thereby developing a shrinkage difference between both the yarns. However, the elongation difference can sufficiently not be enlarged even by this method, although the boiling water shrinkage difference is enlarged. Therefore, the finally obtained woven or knitted fabric does still not have a satisfiable touch (texture).
Further, in JP-A 8-209442 is described a blended yarn which comprises two filament groups comprising highly shrinkable filaments and low shrinkable filaments whose heat shrinkage factors are different from each other and which have a shrinkage difference of 5 to 25%, wherein the low shrinkable filaments comprise a polyester, and the highly shrinkable filaments comprise a copolymerized polyethylene terephthalate obtained by copolymerizing specific amounts of three kinds of monomers consisting mainly of isophthalic acid and two kinds of hydroxyethoxyphenols. Although surely giving a sufficient shrinkage difference, the copolymerization of the third component does always not mean to develop sufficiently large elongation difference. In addition, It is difficult to say that the obtained blended yarn is a low-cost blended yarn having excellent productivity, and the copolymerized polyethylene terephthalate is inferior in polymerization productivity due to the point of the copolymerization of the third component consisting mainly of the isophthalic acid, and is therefore undesirable.
In JP-A 60-126316 is also described a method for producing a polyester blended yarn, comprising melt-extruding two or more polyester filament groups from an identical spinning pack, using a stepped roller having different surface speeds at an identical rotating speed to develop a spinning speed difference between the two filament groups, taking off the filament groups so that the filament group low in the spinning speed is drawn between the stepped roller and the next roller and so that the filament group high in the spinning speed is not drawn, doubling and interlacing both the filament groups with an interlacing device, and then winding up the blended yarn at a speed of not less than 100 m/min. However, in this method, devices and operation conditions are complicated, and it is difficult to realize a stable operation over a long period. Further, the range of production conditions enabling the practical production of the polyester blended yarn is narrow, and it is difficult to obtain the blended yarn having such a shrinkage difference as sufficiently developing bulkiness after false-twisted.
In JP-A 7-243144 is described a method for imparting water to one filament group among plural melt-extruded filament groups, not imparting water to the other filament group in a non-bundled state, simultaneously allowing both the filament groups to pass through heating cylinders set at not less than 150° C., respectively, taking off the filament groups at a speed of 3,000 to 5,500 m/min, and then doubling and blending the filament groups. In this method, it is difficult to uniformly heat the filament groups traveling at the high speed, and the produced blended yarn has many quality irregularities and does not give a woven fabric having a high commercial value.
On the other hand, as a method for spinning and blending two or more, kinds of filaments having an elongation difference therebetween, in JP-A 57-61716 is described a method for spinning and blending a filament group comprising a mixture obtained by adding a polymethyl methacrylate-based polymer and/or a polystyrene-based polymer to a substrate polymer containing a polyester as a main component, and a filament group comprising the substrate polymer. This method is surely a profitable method, because the blended yarn having a shrinkage difference between the filament groups can be produced from only the usually available polymers by use of a concise spinning device. Additionally, remarkable is the technology that the fine division process of the filament group spun from the mixture obtained by adding a polymer such as the polymethyl methacrylate or the polystyrene to the polyester is different from that of the filament group simultaneously spun from only the polyester, consequently developing a shrinkage difference between both the filament groups. However, the method has a problem that the filament group is frequently broken to lower the productivity of the filament group, when the filament group is spun and wound up only in conditions described in the method. Thereby, also in the technology that the polymer such as the polymethyl methacrylate-based polymer and/or the polystyrene-based polymer is added to the polyester to develop a physical property difference between the filament group spun from the polymer mixture and the filament group simultaneously spun from only the polyester, devices are further needed for the stable commercial production of the desired blended yarn for a long period.
Further, in JP-A 58-98418 is also described a method for producing the same spun blended yarn as that in the above-described specification. The blended yarn obtained by this method is relatively good at the point of bulkiness, but insufficient at the point of texture (softness, repulsiveness, swelling, and the like). Thereby, the development of a technology for further improving such texture is desired. Additionally, the stability of the production is also insufficient in this method, and the further improvement of the technology is demanded.